This application claims the benefit of the Korean Application No. P2000-84717 filed on Dec. 28, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a projector.
2. Background of the Related Art
The projector enlarges, and projects a small picture on a small display inside of the projector by using a projection lens system to a large sized screen, to display a large sized picture. There are a front projection type in which the picture is displayed on a front face of the screen, and a rear projection type in which the picture is displayed on a rear face of the screen. As a typical one of the latter, there is the projection television. As the small display in the projector that displays the small picture, LCD (Liquid Crystal Display) and DMD (Digital Micromirror Device), and the like are employed. The LCD is provided with a polarization beam converter as shown in FIGS. 1A and 1B for displaying the picture by using a linearly polarized light.
In order to fabricate a small sized projector, and enhance a visibility of the large picture displayed on the large sized screen, it is required to fabricate the polarization beam converter thinner, as well as minimize an optical loss of the polarization beam converter.
FIGS. 1A and 1B illustrate related art polarization beam converters, FIG. 2 illustrates operation of the polarization beam split array in FIG. 1A, FIGS. 3A and 3B illustrate details of the polarization beam sprite array in FIG. 1A, FIG. 4 illustrates a light source with a parabolic reflector, FIG. 5 illustrates a light source with an elliptic reflector, and FIG. 6 illustrates a beam distribution of beams focused by the lens array in FIG. 1A.
Referring to FIGS. 1A and 1B, the related art polarization beam converter is provided with a first lens array 2, a second lens array 4, and a polarization beam split array 6 facing an optical output surface of the second lens array 4.
The first lens array 2, or the second lens array 4 focuses white beams of lights inclusive of P wave and S wave onto a plurality of focusing points. As shown in FIG. 6, light beams 15 pass through the lens array shown in FIG. 1A. To do this, the first, or second lens array 2, or 4 has a matrix of a plurality of lenses.
In the meantime, the polarization beam split array 6 transmits an xe2x80x98Sxe2x80x99 wave, and converts a xe2x80x98Pxe2x80x99 wave into xe2x80x98Sxe2x80x99 wave and transmits the converted xe2x80x98Sxe2x80x99 wave among the beams from the second lens array 4. To do this, the polarization beam split array 6 has polarization beam split planes 10 and polarization beam reflection planes 12, both sloped with respect to an optical input surface and an optical output surface as shown in FIG. 2, and half wavelength plates 8 attached to the optical output surface.
The polarization beam, split plane 10 only transmits the P wave and reflects the S wave among the white beams of lights from the second lens array 4. The P wave passed through the polarization beam, split plane 10 is converted into an S wave by the half wavelength plate 8. On the other hand, the S wave reflected at the polarization beam split plane 10 is reflected at the reflection plane 12.
That is, the entire beams of lights inclusive of the P wave and the S wave passed through the polarization beam split array 6 are converted into the S wave. The polarization beam split array 6 has two parts to be symmetric with respect to a center art 14 thereof as shown in FIG. 3A.
Referring to FIGS. 3A and 3B, the white beams of lights incident on the first lens array 2 from the light source (not shown) are incident on the first lens array in parallel to one another. To do this, the related art polarization beam converter employs a lamp 18 with a parabolic reflector 16. However, even the white beams from the lamp 18 with the parabolic reflector 18 include non-parallel beams. As shown in FIG. 3B, the second lens array 4 serves to compensate for a loss caused by the non-parallel beams.
The lamp 18 with the parabolic reflector 16 has an optical efficiency poorer than a lamp 20 with an elliptic reflector 22 shown in FIG. 5.
It will be explained in detail, assuming that a diameter of the parabolic reflector 16 is Dp and a diameter of the elliptic reflector is De. The lamp 18 with the parabolic reflector 16 directs the beams of lights forward in parallel, i.e., the parabolic reflector 16 is required to have a slope for directing the beam from the lamp 18 forward in parallel.
On the other hand, the lamp 20 with an elliptic reflector 22 directs the beams of lights such that the beams are focused at a plane in front of the lamp 20. Accordingly, the elliptic reflector 22 is required to have a slope greater than the parabolic reflector 16 so that the beams from the lamp 20 are focused on the plane in front of the lamp 20. That is, because the lamp 20 with the elliptic reflector 22 can reflect more beams, the lamp 20 with the elliptic reflector 22 has an optical efficiency higher than the lamp 18 with the parabolic reflector 16.
If the lamp 20 with the elliptic reflector 22 and the lamp 18 with the parabolic reflector 16 have the same optical efficiency, the diameter of the elliptic reflector 22 can be made smaller than the parabolic reflector 16, to reduce a size of the elliptic reflector 22. However, since the related art projector requires parallel beams, the lamp 20 with the elliptic reflector 22 can not be employed therein. Therefore, the related art projector has a limitation in fabricating a thinner projector.
Moreover, there are no beams incident on a center part of the related art polarization beam split array 6. That is, the beams from the first lens array 2 and the second lens array 4 are incident on the polarization beam split array 6 in symmetry with respect to a center part 14 thereof. Consequently, no beams pass through the center part 14 of the related art polarization beam split array 6. Accordingly, there has been a problem in that a uniformity of the beams becomes poorer even if a position of the polarization beam split array 6 is changed, slightly.
Furthermore, the related art polarization converter is provided with lens arrays having a plurality of lenses. There are optical losses between the plurality of lenses of the lens arrays. However, if the number of the lenses provided in the lens array is reduced, a production cost of the projector increases because a thickness of the polarization converter relatively increases. Particularly, since alignment of the lens arrays influences to an optical conversion efficiency significantly, much time is required for an accurate assembly.
In addition to this, because the related art projector uses parallel beams, the beams are not focused at one point. Therefore, in order to employ only one sheet of display (i.e., for providing a color wheel), a first optical system for focusing the beams, and a second optical system for diverging the focused beams again are required, additionally. Accordingly, the fabrication of a thinner projector has been difficult in the related art.
Accordingly, the present invention is directed to a projector that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a projector which permits fabrication of a thinner projector.
Another object of the present invention is to provide a projector which can minimize an optical loss.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the projector employs a rod lens for making a distribution of incident beams uniform. The employment of the rod lens permits to employ a lamp with an elliptic reflector that allows fabrication of a thin projector.
In another aspect of the present invention, there is provided a projector including a light source for emitting beams of lights, a rod lens for receiving the beams of lights from the light source and making a distribution of the beams uniform, and a polarization beam converter for receiving the beams from the rod lens. The polarization beam converter has a lens part for receiving the beams from the rod lens and focusing onto a plurality of focusing points, and a polarization beam split array receives the beams inclusive of a P wave and an S wave, and forwards the P wave as it is, and converting the P wave into the S wave before forwarding.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.